Kachina 505DSP PLL problem

The Kachina 505DSP is one of the very finest American made HF-radios.

Unfortunately these are no longer in production and the few ones left in the field may quit due to a crystal aging problem. The reference oscillator tuned by a varicap and normally locked to WWV slowly gets out of its locking range and then suddenly starts seeking.

The symptom is that the radio starts jumping up and down around the wanted frequency, and the automatic calibration procedure no longer works.

The cure is simple, but you have to do some minor modifications to the radio, as without extention boards it is not possible to realign the oscillator. The trim capacitor is inaccessible when the board is in its normal position.

Pull out the PLL board PC301. Open the little box on the left containing the oscillator with the aging crystal Y302. Remove the (otherwise inaccessible) ceramic trim capacitor C1312 (2.5-10 pF) and replace it by a Johansson screw type and solder it to the partly removed wall of the tin box. Connect a little measurement wire to TP-2.

Re-install the board and connect a voltmeter to the wire connected to TP 2. You will see the voltage going up and down between 1 and 4 volts (sawtooth PLL seek cycle). Adjust the newly installed trim capacitor until you have about 2.5 volts. The radio is locked again now. Perform a software frequency calibration on WWV 10 MHz and readjust the voltage again until you have 2.5 volts again.

Close the box and start ragchewing... you do own a working radio again, one of the very best ever American made.